1. Technical Field
The present invention relates to a bonded structure including a first substrate in which a first electrode layer is formed and a second substrate in which a second electrode layer electrically connected with the first electrode layer is formed, a piezoelectric device and a liquid ejecting head which include the bonded structure, and a method of manufacturing the bonded structure.
2. Related Art
A bonded structure in which a first substrate having a first electrode layer and a second substrate having a second electrode layer are bonded with each other in a state of being electrically connected is built into various electronic devices. For example, a piezoelectric device which is a type of the bonded structure is applied to various liquid ejecting apparatuses, vibration sensors, and the like. Such a piezoelectric device is provided with a piezoelectric element in one of the first substrate and the second substrate described above, and allows the piezoelectric element to function as an actuator, a sensor, or the like. For example, in the liquid ejecting apparatus, the piezoelectric device is built into a liquid ejecting head, and liquid is ejected from a nozzle formed on the liquid ejecting head by driving the piezoelectric element.
In addition, as such a liquid ejecting apparatus, for example, an image recording apparatus such as an ink jet type printer, an ink jet type plotter, or the like is used. Recently, the liquid ejecting apparatus is also used for various manufacturing apparatuses by utilizing an advantage thereof that a very small amount of liquid is capable of being accurately landed onto a predetermined position. For example, such liquid ejecting apparatus is applied to a display manufacturing apparatus for manufacturing a color filter of a liquid crystal display or the like, an electrode forming apparatus for forming an electrode of an organic electro luminescence (EL) display, a field emission display (FED), or the like, and a chip manufacturing apparatus for manufacturing a biochip (biochemical element). A recording head for an image recording apparatus discharges liquid type ink, and a color material discharging head for a display manufacturing apparatus discharges a solution of each color material of red (R), green (G), and blue (B). In addition, an electrode material discharging head for an electrode forming apparatus discharges a liquid type electrode material, and a bio organic material discharging head for a chip manufacturing apparatus discharges a solution of bio organic material.
The first electrode layer of the first substrate and the second electrode layer of the second substrate in the bonded structure described above are electrically connected to each other through a bump. In a case where both electrodes are electrically connected through such a bump, in order to reliably connect the bump with the electrode layer facing the bump, pressure is applied when the first substrate and the second substrate are bonded to each other. In this state, the first substrate and the second substrate are bonded. In addition, as an adhesive for bonding the first substrate and the second substrate to each other, an adhesive having photosensitivity is used because it is possible to form a high precision pattern by suppressing wetting and spreading (for example, refer to JP-A-2000-289197).
When the first substrate and the second substrate are bonded to each other, if the photosensitive adhesive before bonding is excessively hard, there is a concern that a bonding force between both the substrates after bonding is deteriorated. Meanwhile, if the photosensitive adhesive before bonding is excessively soft, there is a concern that pressure is focused on the bump at the time of bonding both the substrates, and a shape of the bump is deformed or broken. Particularly, in a case where a resin core bump is used in which a part of the electrode layer is stacked on a surface of a resin portion having elasticity, as the bump, there is a concern that the electrode layer stacked on the surface of the resin portion is disconnected.